The field of the present invention is lasers and their methods of use, and more particularly, pulsed lasers and their use in medical, dental, and industrial applications.
Recently, a number of pulsed lasers have been developed for use in medical, dental, and industrial applications. For example, those skilled in the art will note that pulsed laser systems are commonly provided in three forms: flashlamp pumped free-running, flashlamp pumped electro-optically (E-O) Q-switched, and continuously pumped acousto-optically (A-O) Q-switched. Further, it will be noted by those skilled in the art that the neodymium doped yttrium aluminum garnet (Nd:YAG) laser, a laser which has been adapted for use in numerous medical and dental applications, is exemplary of pulsed laser systems.
When the Nd:YAG laser is provided as a flashlamp pumped free-running system, a flashlamp pulse having a duration typically between 100 and 1000 .mu.s pumps the Nd:YAG rod of the laser, and a laser output pulse of approximately the same duration is produced. Flashlamp pumped laser pulse energies are commonly in the 1-1000 mJ range, and for this reason the maximum peak laser output power of a flashlamp pumped free-running system is typically 10 kW.
For certain applications, however, those skilled in the art will note that peak output powers greatly exceeding 10 kW may be desired, and that, in response to this need, a number of flashlamp pumped E-O Q-switched Nd:YAG lasers have been developed. The flashlamp pumped E-O Q-switched Nd:YAG laser utilizes an electro-optical Q-switch to disrupt beam oscillation within the oscillating cavity of the laser during the entire duration of each flashlamp pulse, and to restore beam oscillation immediately following each flashlamp pulse. In this fashion, substantially all of the flashlamp pulse energy is stored in the Nd:YAG rod during the duration of each flashlamp pulse, and upon the restoration of beam oscillation within the oscillating cavity a "giant pulse" laser output is produced. More specifically, as beam oscillation is restored, substantially all of the energy stored within the Nd:YAG rod is extracted from the rod in the form of a single giant pulse having a duration of approximately 10 ns. In this way, laser output pulses having peak powers in the range of 100 MW may be readily produced. Unfortunately, laser output pulses having peak powers in the 100 MW range are not useful in many applications, and in particular, laser output pulses having peak powers in 100 MW range cannot be carried by conventional fiber optic delivery systems. While laser output pulses having lower peak powers may be obtained from a flashlamp pumped E-O Q-switched Nd:YAG laser by reducing the amount of energy contained in each flashlamp pump pulse, the difficulty of operating E-O Q-switches at high repetition rates (i.e. 100 Hz or better) makes it impractical to achieve desirable peak powers while at the same time maintaining an average laser output power of between 5 and 50 W.
Finally, in contrast to flashlamp pumped Nd:YAG pulsed lasers, continuously pumped A-O Q-switched Nd:YAG pulsed lasers, such as the laser disclosed and claimed in U.S. Pat. No. 4,273,535, issued to Yamamoto et al., and entitled "Device for Preventing Tooth Decay by Laser Beam Irradiation and Method of Preventing Tooth Decay by Means of the Same," typically utilize an arc lamp to continuously pump the Nd:YAG rod, and utilize an A-O Q-switch to periodically trigger energy storage and release by the Nd:YAG rod. The storage time and pulse repetition rate can be adjusted over a broad range. However, to maximize laser output pulse peak powers it is necessary to maximize energy storage within the Nd:YAG rod prior to switching. This is accomplished by setting the rate of triggering in accordance with the lifetime of the excited state of the Nd:YAG rod. However, those skilled in the art will appreciate that, as the pulse repetition rate is reduced, the efficiency of a conventional laser is sacrificed, and the average power generated by the laser decreases. If on the other hand, the pulse repetition rate is increased, the peak powers generated by the conventional laser will decrease, thus inhibiting any increases in the average power of the laser. For these reasons, it is impractical using conventional laser systems to generate laser output pulses having desirable peak powers, while at the same time maintaining an average laser output power in the range of 5-50 W.
Because it is desirable in many applications to generate laser output pulses having peak powers in the 10 -1000 kW range, while at the same time maintaining laser efficiency of 1 to 2% or more and maintaining a pulse repetition rate in the range of 10-200 Hz, a new laser system is desired.